1. Field of the Invention
The present invention relates to a charging device used in an image forming apparatus with the use of an electrophotographic system.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-072212 discloses a technology of suppressing increase in the amount of a deposited electric discharge product on a charger shutter by making the charger shutter contain a photocatalytic substance, and irradiating the charger shutter having the electric discharge product deposited thereon with a light which causes a photocatalytic reaction to thereby decompose the electric discharge product. Japanese Patent Application Laid-Open No. H07-104564 discloses a charger shutter which uses a stainless steel containing 2 to 20 wt % or more of nickel (Ni) for the charger shutter; and describes that the charger shutter thereby makes nitric acid or a nitrate ion which is an electric discharge product combine with Ni to form a metal salt, makes the stainless steel form a passive state thereon against nitric acid, and can improve an image deletion phenomenon even when the electric discharge product has deposited on the charger shutter.
However, in the configuration according to Patent Japanese Patent Application Laid-Open No. 2007-072212, the charger shutter having the electric discharge product deposited thereon is irradiated with the light which causes the photocatalytic reaction, and accordingly the charging device needs a space into which the charger shutter retreats from underneath the corona charger, and needs to provide a light source therein having such a wavelength component as to excite the photocatalytic substance. Usually, when a tabular charger shutter is moved in a sub-scan direction, there is a pre-exposure (discharging member) region in the upstream side of the corona charger and there is an image exposure region in the downstream side. Therefore, in order to configure the evacuation space and the light source while avoiding those regions, the arrangement of the devices is complicated, which may result in an increase in costs.
As for the configuration according to Patent Japanese Patent Application Laid-Open No. H07-104564, since the passivated nickel hardly forms a metal salt with nitric acid or a nitrate ion, the nitric acid produced on the charger shutter gradually becomes hard to convert into the metal salt.
According to the investigation by the present inventors, the charger shutter according to Japanese Patent Application Laid-Open No. H07-104564 had some cases in which the nitric acid that was not converted into the metal salt resulted in remaining on the surface of the charger shutter for a long period of time, the nitric acid migrated to a photosensitive member or caused image deletion and the improvement effect could not be fully obtained for the problem that the image deletion phenomenon occurred in an electrophotographic image due to the electric discharge product.
For this reason, the present invention is directed to provide a charging device which can suppress the influence that an electric discharge product having deposited on the charger shutter gives to a photosensitive member for a long period of time, and as a result, can suppress the deterioration of the photosensitive member and the occurrence of the image deletion phenomenon on an electrophotographic image, for a long period of time.